Seamless tube mill piercer mandrel and assembly

ABSTRACT

A laminate tube structure produced by stretch reducing, in combination, a pair of tubes. The resultant tube structure is particularly adapted for use as a mandrel for supporting a piercing point of a seamless-tube mill.

United States Patent Reiley et al.

[ Nov. 11, 1975 SEAMLESS TUBE MILL PIERCER MANDREL AND ASSEMBLY Inventors: Bertrand M. Reiley, Canfield; Edwin J. Muccillo, Youngstown; Robert G. Griffith, Poland, all of Ohio Assignee: Youngstown Sheet and Tube Company, Youngstown, Ohio Filed: Oct. 29, 1974 Appl. No.: 518,363

Related US. Application Data Division of Ser. No. 352,928. April 20. 1973, Pat. No. 3.882,595.

US. Cl 72/97; 72/208 Int. Cl. B21B 25/00 Field of Search 29/474.3, 155 C; 72/209,

[56] References Cited UNITED STATES PATENTS 860.232 7/l907 Offutt 29/474.3 1.989.507 l/l935 Diescher 72/209 X 2.025.439 12/1935 Brownstein 72/208 X 2,167,424 7/l939 Novack 72/209 X 2.742.946 4/1956 McGrann 29/155 C Primary Examiner-Milton S. Mehr Attorney, Agent, or Firm-John Stelmah [57] ABSTRACT A laminate tube structure produced by stretch reducing, in combination, a pair of tubes. The resultant tube structure is particularly adapted for use as a mandrel for supporting a piercing point of a seamless-tube mill.

2 Claims, 5 Drawing Figures US. Patent Nov. 11, 1975 3,918,284

INSERT ONE TUBE 7 Y HEAT STRETCH wm-uu COMBINATION REDUCE ANOTHER COMBINATION W INSERT AND SECURE CROP AND PIERCER POINT cur T0 LENGTH SEAMLESS TUBE MILL PIERCER MANDREL AND ASSEMBLY This is a divisional application of copending application Ser. No. 352,928, filed Apr. 20, 1973, now US. Pat. No. 3,882,595.

BACKGROUND OF THE INVENTION This invention relates to a laminate tube structure and method of producing the same in a manner whereby a monocoque-type structure results.

Thisinvention further relates to a method of producing a mandrel which can withstand increased compressive stresses and hence makes it particularly adaptable for supporting a piercing plug of a seamless-tube mill.

This invention also relates to a method of increasing the production rate in a seamless steel mill.

The situation from which the invention was developed was the search for a mandrel structure which can withstand the high compressive forces imposed on the piercer mandrel of a seamless-tube mill.

DESCRIPTION OF THE PRIOR ART Seamless-tube mills usually include a relatively long mandrel which supports and carries the piercer point. A pair of opposing rolls which rotate in the same direction, are positioned at specific angles to the pass centerline. The rolls being set at an angle to the pass line impart two components of force to the billet round as it is forced through the mill. One component imparts a spinning motion to the round while the other component imparts a longitudinal forward motion along the pass line. As the round is fed forward, it contacts the piercer point and the metal of the round flows over and about the point to form the seamless tube. The mandrel is not forced through the round, the metal flows over and about the point and then about the mandrel. As the metal flows over the piercer point, great compressive stresses are imposed on the piercer point and consequently on the supporting mandrel.

The opposing rolls are positioned with each respective axis being inclined generally about 6 to' 12 with the pass line of the seamless mill. The larger angles are employed in conjunction with the production of relatively large diameter tubes, i.e., those with outside diameters greater than 7 inches. In conjunction with some of what may be termed intermediate size seamless tubes, e.g., 6 7 inches O.D. tubes, it has been the practice to limit the roll angle of inclination to 8. In such cases, the practical limit of the outside diameter of the mandrel is about 4% inches. It was found that if the 8 angle of inclination was exceeded, a 4% inch mandrel would not withstand the additional stresses and early mandrel failure occured.

OBJECTS AND SUMMARY OF THE INVENTION It is the principal object of this invention to provide a method of producing a laminated tube structure capable of withstanding increased compressive stresses.

It is another object of this invention to provide a mandrel of increased strength, which mandrel is adapted to support a piercing plug in a seamless-tube mill.

It is a further object of this invention to'provide a method and means for increasing the production of a seamless-tube mill.

Briefly, the objects are generally attained by stretch reducing, in combination and into mutually engaging relation, a pair of tubes. As a result a monocoque tube structure is provided having increased resistance to compressive forces and to permanent deflection. The inner tube is inserted within the outer tube and the combination is heated in a furnace and then stretch reduced to cause the two tubes to interface. In an exemplary combination, the outer tube has an outside diameter of 5% inches and a nominal wall thickness of about 0.340 inch, the inner tube has an outside diameter of 4% inches and a nominal wall thickness of about 0.310 inch. The desired monocoque, mandrel outside diameter may be selectively produced by controlling the amount of stretch reduction. Mandrels having outside diameters from 3% to 4% inches have been produced from the above-described typical combination. The monocoque tube structure provides an arrangement wherein stress imposed upon one of the tubes is shared by the other. Although it is not necessary, it is preferred that one or both of the tubes comprising the mandrel be of the seamless type.

DESCRIPTION OF THE DRAWING The invention will be more fully understood and further objects and advantages thereof will become apparent when reference is made to the following detailed description and to the accompanying drawing, in which:

FIG. 1 is a fragmentary cross-sectional view of a laminated tube structure embodying this invention and shown as a mandrel in a mandrel assembly of a scamless-roll mill;

FIG. 2 is a block diagram illustrating the process steps for producing the laminated tube structure of FIG. 1;

FIG. 3 is a schematic representation illustrating the stretch rolling action of a stretch mill;

FIG. 4 is a schematic elevational view of a heated billet round being pierced by the piercing point between piercing rolls; and

FIG. 5 is a plan view of the piercing rolls of FIG. 4, illustrating the angles of the rolls in respect to the advancing or pass line of the tube mill.

DESCRIPTION OF A PREFERRED EMBODIMENT This invention is particularly adapted for producing mandrels for use in conjunction with piercing operations in a seamless-tube mill and will be described in that connection. However, it will be understood that the principles can be applied to other tube structures,

, such as for example, drill pipe, high strength transmission line pipe.

Referring to FIG. 1 of the drawing, the piercer mandrel assembly 10 comprises a mandrel bar 12, a bar cap 14 and a piercer point 16. The mandrel bar 12 is hollow in order to accommodate passage of a coolant. The mandrel 12 comprises a laminate wall structure formed by joining tubes 12A and 123 into mutually engaging relation. The piercer point 16 is suitably secured to bar cap 14, e.g., by welding. The bar cap 14, in turn, is inserted within the mandrel l2 and suitably fastened to restrict longitudinal movement in respect to the man- -drel 12, such as by bolt 18. The cap 14 is also provided with an end flange portion 20 to mate with correspond- 3 rolls.

In a representative embodiment of this invention, a first tube, designated as inner tube 128, is inserted inside a second tube, designated as outer tube 12A. Typically, the inner tube 12B may have an outside diameter of 4% inches and a nominal wall thickness of about 0.310 inch; also, the outer tube 12 may have an outside diameter of 5% inches and a nominal wall thickness of about 0.340 inch. The combination of tubes 12A and 12B is heated to hot working temperatures in a furnace having a temperature of about 1,950F. The combination is then stretch reduced in a mill (FIG. 3) to cause the inside circumference 12AC of tube 12A and the outisde circumference 12BC of tube 123 to interface, and to form a laminate structure of preselected size. If a laminate structure having an outside diameter of about 4% inches is selected, the resultant nominal wall thickness will be in the order of 0.600 inches. The temperatures of the tubes at the time of rolling in the stretch mill are in the order of about l750F for the outer tube 12 and about 1550F for the inner tube 12B.

The size is determined by controlling the degree of reduction and stretching on the stretch reducing mill. Laminate structures from the above described typical combination of tubes have been produced, which structures have outside diameters of 4%, 4, 3 /8 and 3% inches. However, it will be understood that other combinations of tube sizes and that tubes having steel compositions other than the typical exemplary composition now set forth may be used:

Typical composition: (indicated percentages, by weight) Carbon .37 .42 Manganese 1.40 1.60 Phosphorus .020 max. Sulfur .030 max. Silicon .20 .28 Molybdenum .16 .20 Aluminum .020 .080 The remainder being iron with ordinary impurities.

Although the laminate monocoque construction of this invention provides the potential for increasing the strength of all sizes of tube structures, the construction is of particular utility and significance in the production of tube structures which are employed as mandrels whose outside diameters must be restricted to 4% inches, or less.

Seamless-tube mills usually include a relatively long mandrel 12, e.g., in excess of feet long, which supports and carries the piercer point 16, as shown in FIG. 1. A pair of opposing rolls and 32 are positioned at specific angles (hereinafter described) to the mill center pass line CL. The rolls 30 and 32 are positioned so that each respective axis is oblique to pass line CL and thus the rolls impart two components of force to the metal of the billet round as it is forced through the mill. One component imparts a spinning or rotational motion while the other component imparts a longitudinal forward motion along the line CL. As the billet round is advanced, the resistance of the piercer point causes the metal to flow over and about the point and thus form the tube. It is to be noted that the piercer mandrel is not forced through the round but that the billet metal flows over and about the point and then around the mandrel. The tubes are made from billet rounds which generally range in length from about 86 to about 200 inches. As

the length of the billets increase, the time of contact of the metal of a single billet with the piercer point is correspondingly increased as is the temperature of the piercer point. With repetitive piercing under such conditions, the piercer point loses its effectiveness and more compressive stress is imposed upon the support mandrel. Thus, a mandrel of increased strength capable to withstand the increased pressure forces would contribute substantially toward increasing the effective life of the piercer mandrel assembly 10. As will be apparent from FIG. 4, these pressure forces are in the nature of axial compressive forces, i.e., those which would tend to bow a mandrel as opposed to radial compressive forces such as those encountered in rolling mill mandrels and practices wherein wall-reducing rolls exert radial pressure upon the tube support mandrel.

As indicated above, the opposing rolls 30 and 32 are positioned with each respective axis being inclined with the pass line CL of the mill. The angle of inclination d) is generally in order of 6 to 12 The larger angles, 9 to 12, are employed in conjunction with the production of relatively large diameter tubes, i.e., those with outside diameters greater than 7 inches. In the production of intermediate size seamless tubes, i.e., those with outside diameters of 6 to 7 inches, it has been the practice to limit the angle of inclination of the roll to 8. With such sizes, the practical limit of the piercer mandrel outside diameter is in the order of about 4% inches because of the internal space available within the tube being formed. It was found, with the use of an ordinary mandrel with an outside diameter of about 4% inches, that if the angle of inclination is exceeded beyond 8 the mandrel falls comparatively early because of the additional imposed compressive stress. With an increase in angle the forward motion component force of the rolls is increased.

Through the use of the improved mandrel, this invention provides a method of increasing the production of a seamless-tube mill. Because of the ability of the mandrel to withstand increased forces, the angle of inclination of the piercing rolls may be increased, e.g., in the production of intermediate size tubes, the angle d) may be increased to 9 to l l%; as the angle of inclination is increased, the component of force contributing to the longitudinal forward motion of the billet round is increased and moves the metal faster over the piercer point. Thus it takes less time to move all of the metal of an individual billet over the point. The fact that the metal is in contact with the piercer point for a shorter time 'also contributes toward increased life of the piercer point.

What is claimed is:

1. A seamless tube mill piercer point mandrel assembly comprising a piercer point and a support mandrel for said piercer point, and wherein the outside diameter of said piercer point is greater than the diameter of said support mandrel, the improvement wherein:

said support mandrel is a composite structure formed by stretch reducing the combination, when at hot working temperature, of a first tube over a second tube,

the tubes of said composite structure being of substantially the same length, and

said mandrel having increased resistance to axial applied compressive forces.

2. In a seamless tube mill piercer point support mandrel, the improvement wherein:

. tubes; and said mandrel IS a composite structure of two tubes of Said pp mandrel having means defining a g substantially equal length, clutch portion for mating with a corresponding dog clutch portion of a bar cap.

said composite structure is formed by stretch reducing the combination, when a hot working temperature, of a first of said tubes over the second of said 

1. A seamless tube mill piercer point mandrel assembly comprising a piercer point and a support mandrel for said piercer point, and wherein the outside diameter of said piercer point is greater than the diameter of said support mandrel, the improvement wherein: said support mandrel is a composite structure formed by stretch reducing the combination, when at hot working temperature, of a first tube over a second tube, the tubes of said composite structure being of substantially the same length, and said mandrel having increased resistance to axial applied compressive forces.
 2. In a seamless tube mill piercer point support mandrel, the improvement wherein: said mandrel is a composite structure of two tubes of substantially equal length, said composite structure is formed by stretch reducing the combination, when a hot working temperature, of a first of said tubes over the second of said tubes; and said support mandrel having means defining a dog clutch portion for mating with a corresponding dog clutch portion of a bar cap. 